1. Field of the Invention
This invention relates generally to rod rolling mills, and in particular to an improved laying pipe for use in the laying heads of such mills.
2. Description of the Prior Art
Mill builders are constantly striving to increase mill delivery speeds in order to maximize the productive capacity of the mill equipment. For example, ten years ago a mill delivery speed of 50 meters/sec. for 5 mm. rod was considered "fast". However, the same product is being rolled currently at mill delivery speeds as high as 112 meters/sec. and still further speed increases are being contemplated.
These increases in mill delivery speeds have given rise to serious problems with regard to the design and maintenance of the laying pipes used in the laying heads. Again by way of example, if 5 mm. rod being delivered at a speed of 112 meters/sec. is to be formed into 1125 mm. diameter rings, the laying pipe must rotate at a speed of 1900 rpm. Under these conditions, the laying pipe is subjected to severe rotational stresses. However, a pipe material selected primarily for its ability to withstand such stresses often lacks the ability to adequately resist internal frictional wear without marking the surface of the product passing therethrough.
An attempt at solving this problem is disclosed in U.S. Pat. No. 4,074,553 where the laying pipe consists of an outer three-dimensionally curved tube lined with a plurality of replaceable inserts. The material from which the outer tube is fabricated is selected primarily for its ability to withstand rotational stresses, whereas the material for the replaceable inserts is selected for its ability to resist frictional wear without marking the surface of the mill product. Although this approach appeared to be theoretically sound, the relative complexity and high cost of the design prevented it from being put into actual practice.